Ceramic metallic interlocked components and methods of making and using the same

ABSTRACT

A composite element is provided. The composite element includes a ceramic component defining a cavity having a first end and a second end, and a metallic component comprising a head and a body. At least a portion of the body of the metallic component is disposed in the cavity, and the head of the component is disposed on the first end of the cavity. A cross-sectional area of a portion of the body is greater than an area of the first end. In addition, the ceramic and metallic components are interlocked. Methods of making a composite element and of making a clearance sensor part are also provided.

CROSS REFERENCE TO RELATED APPLICATION

This Application is a divisional of U.S. patent application Ser. No.12/605,640, entitled “Ceramic metallic interlocked components andmethods of making and using the same,” filed Oct. 26, 2009, now U.S.Pat. No. 8,056,606, which is herein incorporated by reference in itsentirety.

BACKGROUND

The invention relates to composite elements having ceramic and metalliccomponents, and more particularly to ceramic and metallic componentsthat are interlocked and methods of making and using the same.

Various types of sensors have been used to measure the distance betweentwo objects. For example, a turbine has a number of turbine blades thatare disposed adjacent to a shroud. The clearance between one of theturbine blades and the shroud varies depending on various factors, suchas but not limited to, temperature, RPM, load, and age of the turbine.It is desirable that a gap or clearance between the turbine blades andthe shroud be maintained for safe and efficient operation of theturbine. A sensor may be disposed within the turbine to measure thedistance between the turbine blades and the shroud. The measureddistance may be used to direct movement of the shroud to maintain thedesired displacement between the shroud and the turbine blades.

Such sensors typically employ a combination of metallic and ceramiccomponents. The metallic components are partially disposed within theceramic component. Typically, the metallic components and the ceramiccomponents are held together by braze joints. However, since suchclearance sensors are primarily employed in harsh environments (such asinside the engine), the high operating temperatures and pressures arechallenging for the sensor components, and the braze joints. If thebraze joint accidentally fails during the operation, there is a risk ofthe metallic or ceramic component being liberated into the engine, andpossibly damaging the engine.

Accordingly, a need exists for providing a sensor that employs ceramicand metallic components, which will not liberate into the engine duringoperation. It would also be advantageous to provide an economicallyviable method of making such a sensor component.

BRIEF DESCRIPTION

In one embodiment, a composite element is provided. The compositeelement includes a ceramic component defining a cavity having a firstend and a second end, and a metallic component comprising a head and abody. At least a portion of the body of the metallic component isdisposed in the cavity, and the head of the component is disposed on thefirst end of the cavity. A cross-sectional area of a portion of the bodyis greater than an area of the first end, and the ceramic and metalliccomponents are interlocked.

In another embodiment, a method of making a composite element isprovided. The composite element comprises a metallic componentinterlocked with a ceramic component. The method includes providing aceramic component defining a cavity having a first end and a second end,disposing a degradable material in the cavity, and disposing the ceramiccomponent in an investment. The method further includes removing thedegradable material from the cavity, disposing molten metal in thecavity, and solidifying the molten metal to form the metallic component.The metallic component is interlocked with the ceramic component to formthe composite element. The method further includes removing thecomposite element from the mold.

In yet another embodiment, a method of making a clearance sensor part isprovided. The method includes providing a ceramic component defining oneor more cavities for a metallic component, defining one or more cavitiesfor a sensor case on a side of the ceramic component, and disposing adegradable material in the one or more cavities for the metalliccomponent and the sensor case. The method further includes disposing theceramic component in an investment, removing the degradable materialfrom the one or more cavities, and disposing molten metal in the one ormore cavities.

In another embodiment, a composite element formed using the method ofthe present invention is provided.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a diagrammatical illustration of a turbine having a clearancesensor, in accordance with embodiments of the present technique;

FIG. 2 is a cross-sectional perspective view of a composite element of aclearance sensor, in accordance with embodiments of the presenttechnique;

FIGS. 3-4 are schematic flow charts for methods of making compositeelements, in accordance with embodiments of the present technique; and

FIG. 5 is a cross-sectional side view of a composite element disposed ina metallic case, in accordance with embodiments of the presenttechnique.

DETAILED DESCRIPTION

As discussed in detail below, embodiments of the present inventionrelate to composite elements having interlocked ceramic and metalliccomponents and methods of making and using the same. In particular, thepresent technique employs a composite element that does not rely upon abraze joint to hold together the ceramic and metallic components. Incertain embodiments, the composite element includes a ceramic componenthaving a cavity with a first end and a second end, a metallic componenthaving a head and a body, wherein at least a portion of the body of themetallic component is disposed in the cavity, wherein the head of thecomponent is disposed on the first end of the cavity, and wherein across-sectional area of a portion of the body is greater than an area ofthe first end to provide ceramic and metallic components that areinterlocked with each other.

In one non-limiting example, the composite element may be employed in aclearance sensor. Typically, the clearance sensor functions to providean accurate measurement of clearance between two objects in varioussystems such as power turbines (for example, steam or gas/oil-firedpower turbines, or aircraft engines), a generator, a machine havingrotating components and so forth.

FIG. 1 illustrates a rotating machine, such as a turbine 10, wherein theclearance sensor of the present technique can be incorporated to measureclearance between rotating and stationary components. The steam turbine10 includes a rotor 12 disposed within a stationary housing 14. Aplurality of turbine blades 16, which may also be referred to asbuckets, are affixed to the rotor 12. In operation, the blades 16 aresubjected to steam or air at a high temperature and pressure, whichcauses the blades 16 to rotate about an axis. The blades 16 rotatewithin the stationary housing or shroud 14 that is positioned radiallyand circumferentially around the blades 16. A relatively small clearanceexists between the blades 16 and the shroud 14 to facilitate rotation ofthe blades 16 within the shroud 14, while also preventing excessiveleakage of the working fluid, i.e. steam or air, between the blades 16and the shroud 14.

In the illustrated example, one or more clearance sensors, such asrepresented by reference numerals 18, 20 and 22 are disposedcircumferentially around the stationary shroud 14. In the illustratedexample, each of the clearance sensors 18, 20 and 22 may include aplurality of probe tips configured to generate signals representative ofa sensed parameter corresponding to the blades 16. In an exemplaryembodiment, the clearance sensors 18, 20 and 22 are capacitive probesand the sensed parameter is capacitance. In another example, theclearance sensors 18, 20 and 22 are eddy current sensors and the sensedparameter is an induced current. Each of the sensors 18, 20 and 22 maybe configured to generate a signal indicative of a radial and an axialposition of the blades 16 with respect to the shroud 14 at theirrespective circumferential locations.

FIG. 2 illustrates an example of a clearance sensor 28 employing pair ofelectrode tips 30, 32 within a casing 33, and disposed in closeproximity to the turbine blades. The electrode tips 30, 32 may be asingle piece formed by casting a molten metal as will be described indetail with regard to FIGS. 3 and 4. The electrode tips 30, 32 definevias 34 and 36 to receive high temperature instrumentation cables 38 and40 into the cavity to form electrodes. The diameter of the vias 34 and36 typically depends on the diameter of the cables 38 and 40, and thedesired wall thickness at the braze region.

A ceramic component 42 is used to house a portion of the electrode tips30, 32. The ceramic component 42 may comprise a high temperature ceramicsuch as alumina. The ceramic component 42 along with the electrode tips30, 32, forms a composite element having interlocked ceramic-metalliccomponents.

Typically, the electrode tips of such sensors are brazed into a ceramiccomponent. During operation, if the braze joint fails the electrode tipsmay slide through the ceramic component, and possibly be accidentallyliberated in the engine. Advantageously, the shape of the electrode tips30, 32 of the present technique enables the electrode tip to beinterlocked with the ceramic component 42. In other words, the shape ofthe electrode tip 30 prevents the tip 30 from liberating into the engineduring operation. At least a portion 46 of the electrode tips 30, 32 hasa cross-sectional area that is greater than the cross-sectional area ofthe opening 48 in the ceramic component 42, which prevents the electrodetip 30 from coming out of the ceramic component 42.

The electrodes are connected electrically to a voltage source capable ofsupplying a positive or negative voltage on demand. In one example, oneelectrode is polarized to a positive voltage and other to a negativepotential relative to the outer metallic case 33 of the sensor 28. Inoperation, the clearance sensor 28 measures the distance between the tipof a turbine blade and the sensing tips 30, 32 of the electrodes bymonitoring the capacitance of the air gap between the two.

An example process of operating a clearance measurement system includesreceiving a plurality of signals from a sensor having one or more probetips. The signals are representative of a sensed parameter between firstand second objects (for example, between the turbine blades and theshroud). In one embodiment, the sensor is a capacitive probe and thesensed parameter is capacitance. Alternatively, the sensor is an eddycurrent sensor and the sensed parameter is an induced current. Aplurality of simultaneous subsets of sensed parameters are formed. Inone example, each simultaneous subset includes sensed parameters from atleast two probe tips. Further, the clearance between the first andsecond objects may be estimated based upon each of the simultaneoussubsets of the sensed parameters from the probe tips via a processingunit. In certain embodiments, a look-up table, or a calibration curve,or an analytical table, or a calculation, or combinations thereof may beemployed for estimating the clearance based upon the sensed parameters.A processing unit determines the clearance based upon signals from allthe probe tips.

FIG. 3 illustrates exemplary steps in a method of making a compositeelement in accordance with embodiments of the present technique. In theillustrated embodiment, a ceramic component 50 defining cavities 52 isprovided. The cavities 52 are employed to house at least a portion ofthe metallic component that forms the electrode tips. Each of thecavities 52 have a first end 54 and a second end 56. The shape of thecavities 52 in the ceramic component 50 is governed by the desired shapefor the metallic component in the composite element. As described above,the shape of the metallic component may be such that the metalliccomponent is not able to pass through the first end 54 of the cavities52. The shape of the metallic component in the illustrated embodiment isa tapered shape. However, as will be appreciated, other shapes willsatisfy the same criterion and can be employed in the composite element.

A disposable pattern 58 of the metallic component may be disposed in thecavities 52. The disposable pattern 58 may be made of a disposablematerial, such as a wax, polymer, plastic, or combinations thereof. Thedisposable pattern 58 may be formed, for example, using a direct writeprocess prototype, a rapid prototype, an injection molded prototype, diecast prototype, or combinations thereof. Injection molded and die castprototype are more economical and can be employed for simpler shapes. Aswill be appreciated, rapid prototyping is a mostly automated process tocreate a single prototype directly from data. The processes includethree dimensional (3D) printing, fused deposition modeling (FDM), multijet modeling (MJM), thermojet modeling, stereolithography (SLA), andselective laser sintering (SLS). Different kinds of rapid prototypes maybe employed to cast complicated shapes for the metallic component. Inone embodiment, the disposable pattern 58 may be formed of two or moreparts. In the illustrated embodiment, the disposable pattern 58 isformed from two parts, a head 60 and a body 62. The head 60 and the body62 may be joined together after disposing the body 62 in the cavity 52,and the head 60 on the first end 54 of the cavity 52.

Further, in the illustrated embodiment, sprue-forming patterns 66 arecoupled with the disposable pattern 58 so as to leave a passage 67 tointroduce molten metal 68 in the cavities 52 after removal of thedisposable pattern 58. The sprue-forming patterns 66 may be constructedof any lightweight structural material, such as aluminum, magnesium,zinc, steel and other similar metals or their alloys plus selectedplastics. The basic considerations for sprue-forming patterns 66 areweight, surface smoothness, repairability, and compatibility withinvestment 64 and material of the disposable pattern.

Next, investment 64 is disposed around the ceramic component 50 havingthe disposable pattern 58. The ceramic mold employed as investment 64may be produced by repeating steps including coating, stuccoing, andhardening. Coating includes dipping the ceramic component 50 having thedisposable pattern 58 into slurry of fine refractory material andallowing excess slurry to drain off, such that a uniform surface isproduced. The fine refractory material provides a smooth surface finishand reproduces fine details. In the second step, the ceramic component50 having the disposable pattern 58 is stuccoed with a coarse ceramicparticle. Stuccoing may be accomplished by performing one or more ofdipping into a fluidised bed, placing in a rain sander, or by applyingthe coarse particles manually. Subsequent to stuccoing, the ceramiccoating is allowed to harden. The steps may be repeated until theinvestment 64 gains the required thickness. In one embodiment, thethickness of the investment 64 may be in a range from about 5 mm toabout 15 mm. An alternative to multiple dips is to dispose the ceramiccomponent 50 having the disposable pattern 58 in a container and thenpour liquid investment material into the container. In one embodiment,the container may be vibrated (or otherwise agitated) to allow entrappedair to escape and help the investment material fill in all of thedetails. Suitable materials for investment 64 may include but are notlimited to, silica, zircon, alumina, and aluminum silicates.

The investment 64 is then allowed to completely dry. The time period fordrying the investment may depend on the material used in the investment64. In one embodiment, the investment 64 may be dried for a time periodin a range from about 10 hours to about 50 hours. Drying may befacilitated by applying a vacuum or minimizing the environmentalhumidity.

Once the investment 64 has been formed and dried around the ceramiccomponent 50, disposable pattern 58 and sprue-forming patterns 66, theinvestment 64 is then subjected to a treatment for removal of thesprue-forming patterns 66, and the disposable pattern 58 from thecavities 52. The removal of the disposable pattern 58 from the ceramiccomponent 50 leaves behind cavities 52 and 53. The sprue-formingpatterns 66 and the disposable pattern 58 may be removed by anyconventional technique. In one embodiment, the investment 64 may beheated in an inverted position to allow the sprue-forming pattern 66 tobe removed and the material of the disposable pattern to flow out. Thesprue-forming pattern 66 can be re-used with another disposable patternafter it has been removed from the investment 64. Also, the outersurface of the sprue-forming patterns 66 may be coated with a thincoating wax or with a film release agent to facilitate the removal ofthe patterns 66. In certain embodiments, the material of the disposablepattern may be removed by disposing the investment 64 in a furnace orautoclave to melt out and/or vaporize the material of the disposablepattern.

After removal of the disposable pattern 58, the ceramic component 50 hasempty cavities 52 and 53. The desired molten metal 68 for metalliccomponent of the sensor is disposed in the cavities 52 and 53 in theform of a melt. The molten metal may include a single metal, a metalalloy, or a combination of metal alloys. In particular, for applicationsrelating to high temperature clearance sensors, the molten metal 68 mayinclude super-alloys and the platinum group metals and alloys, such asPt—Rh, Pt—Ir. Lower temperature sensors can be fabricated with lowertemperature metals, such as stainless steel, nickel-cobalt-ferrous alloy(for example, Kovar™), and the like. In one example, the cavities 52 and53 may be filled with molten metal by applying negative pressure. Inanother example, the filling of the cavities may be assisted by applyingpositive air pressure, vacuum cast, tilt cast, pressure assistedpouring, centrifugal cast, or centripetal cast. In the embodiment wherethe molten metal is centripetally cast, the rotation per minute (RPM) ofthe investment 64 may be in a range from about 100 to about 500. Forhigh RPMs the metal enters the cavities 52 with turbulence, because ofthe high speeds any sudden change in direction of the molten metal, orany gas obstruction present in the cavities 52 and 53 may shorten thedistance the molten metal can flow. However, by decreasing the RPM orreducing the speed of the machine, the molten metal may enter thecavities 52 and 53 in a smooth even flow, and has the ability to pushany gas from inside the investment 64 and fill the cavities 52 and 53 toprovide clean and porous free castings.

After solidification of the metal, the investment shell 64 is removed toobtain the composite element 70 having the ceramic component 50 andmetallic component 72. The investment 64 may be removed by employing oneor more techniques, such as but not limited to, hammering, mediablasting, vibrating, water-jetting, or chemically dissolving to releasethe composite element 70. The composite element 70 may then be cleanedup to remove signs of the casting process, usually by grinding.

Although not illustrated, final touch-up machining may be required tocomplete the composite element. For example, additional features can bemachined into the cast metal portion of the sensor. Machining ofadditional features may include drilling vias, machining final surfacefinishes, machining mating portions for attachment to the balance of thesensor. For example, vias may be drilled in the metallic component 72.The vias may be employed to receive electronic cable (forinstrumentation cable) for sensing purposes. Alternately, a ceramicshape having the shape of the desired via may be disposed in thecavities 52 prior to disposing the molten metal 68 in the cavities 52.The ceramic shape may be made of a low melting point ceramic relative tothe ceramic of the component 50 so that the ceramic shape can be removedby heating while the ceramic component 50 remains mostly unharmed.

FIG. 4 illustrates an alternate embodiment of a method of making acomposite element according to the present technique. The alternatemethod of FIG. 4 is more suitable for forming metallic components withcomplex shapes. A ceramic component 80 having cavities 82 is provided.For the illustrated example, the cavities have a narrow section 84 and abroad section 86.

The ceramic component 80 may be disposed in an injection mold die 90.The injection mold die 90 defines a head 92 of the metallic component ofthe composite element. A liquid polymer 93 may be then pressure injectedin the cavities 82. The arrow 95 represents the direction of applicationof the pressure to the injection mold die 90. Non-limiting examples ofthe liquid polymer 93 may include liquid vinyl polymer, polyvinylchloride, acrylic resin, or combinations thereof. The liquid polymer 93solidifies after being injected in the cavities 82 to form a plasticpattern 94 of the metallic component.

Next, the ceramic component 80 having the plastic component 94 isremoved from the injection mold die 90. An investment mold 96 isdisposed around the ceramic component 80, while providing feed lines orsprue-forming patterns 97 for the molten metal. The polymer material ofthe plastic component 94 is removed from the cavities. In certainembodiments, the polymer material may be removed from the cavities 82and the head 92 either thermally or by chemical treatment. The polymermaterial is then removed from the cavities by employing methodsdescribed above with respect to FIG. 3.

Molten metal 98 is disposed in the cavities 82 and the head 92. Themolten metal may be disposed by using pressure injection (arrow 99). Anegative or centripetal pressure may be applied to assist in filling themolten metal in the cavities 82 and the head 92. The investment 96 issubsequently removed to obtain composite element 100 having a ceramiccomponent 80 and a metallic component 102.

The broad portion 104 of the metallic component 102 interlocks with theceramic components 80. The interlock prevents the release of themetallic component 102 into the engine during operation.

In one embodiment, the investment mold may be disposed around theceramic component such that the mold defines the cavities around theceramic component. A disposable pattern or a liquid polymer may bedisposed in these cavities outside the ceramic component. In laterstages of the process, the cavities may be filled with molten metal toform a metal case around the composite element of the clearance sensor.

As illustrated in FIG. 5, in certain embodiments, a metallic case 118 isformed around the composite element 122 during the same step as that offorming the metallic component 124 that is interlocked with the ceramiccomponent 120. In these embodiments, a disposable pattern may bedisposed in place for the metallic case 118, and another disposablepattern may be disposed in place for the metallic component 124. Theremaining steps of the method are similar to the method steps describedabove with regard to FIGS. 3 and 4. Metallic component 124 includes ahead 126 and a body 128. The body 128 includes a narrow portion 130 anda broad portion 132. The broad portion 132 having the metallic component124 prevents the metallic component 124 from liberating into the engineduring operation. The ceramic is also interlocked within the outermetallic case 118, as defined by region 134.

The various aspects of the composite element and the methods of makingthe composite element described hereinabove have utility in differentapplications. For example, the composite element illustrated above maybe used for measuring the clearance between rotating and staticcomponents in a power turbine. The resulting composite element may alsobe used in certain other applications, for example, for measuringclearance between stationary and rotating components in generators.Although the present technique has been mostly discussed with regard toclearance sensors, it should be noted that the composite elements of thepresent technique may be employed in several other applications, such asignitors, spark plugs, pressure gauges, and oxygen sensors.

Complicated shapes may be prepared from alloys and superalloys byemploying the above methods by employing suitable techniques such as butnot limited to, injection molding, transfer molding, and the like. Inaddition, the present technique provides an economical way of producingcomposite elements having both ceramic and metallic components.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the scope of the invention.

1. A composite element comprising: a ceramic component defining a cavityhaving a first end and a second end; and a metallic component comprisinga head and a body, wherein at least a portion of the body of themetallic component is disposed in the cavity, wherein the head of themetallic component is disposed on the first end of the cavity, wherein across-sectional area of a portion of the body of the metallic componentis configured to interlock the metallic component with the ceramiccomponent, and wherein the cross-sectional area of the portion of thebody of the metallic component is greater than an area of the first endof the cavity to facilitate interlocking of the metallic component withthe ceramic component.
 2. The composite element of claim 1, wherein thebody has a tapered shape.
 3. The composite element of claim 1, whereinthe head comprises a platinum containing alloy.
 4. The composite elementof claim 1, wherein the body and the head form a single, continuouselement.
 5. The composite element of claim 4, wherein the metalliccomponent is a single piece formed by casting a molten metal.
 6. Acomposite element formed using a method comprising: providing a ceramiccomponent defining a cavity having a first end and a second end;disposing a degradable material in the cavity; disposing the ceramiccomponent in an investment; removing the degradable material from thecavity; disposing molten metal in the cavity; solidifying the moltenmetal to form a metallic component comprising a head and a body, whereinat least a portion of the body of the metallic component is disposed inthe cavity, wherein the head of the metallic component is disposed onthe first end of the cavity, wherein a cross-sectional area of a portionof the body of the metallic component is configured to interlock themetallic component with the ceramic component, and wherein thecross-sectional area of the portion of the body of the metalliccomponent is greater than an area of the first end of the cavity tofacilitate interlocking of the metallic component with the ceramiccomponent; and removing the composite element from the mold.
 7. Thecomposite element of claim 6, wherein the method further comprisesproviding an additional feature in the metallic component.
 8. Thecomposite element of claim 7, wherein the additional feature is machinedinto the metallic component.
 9. The composite element of claim 7,wherein the additional feature comprises a via, and wherein providingthe via comprises: disposing a ceramic shape in the cavity prior todisposing the molten metal in the cavity; and removing the ceramic shapeafter forming the metallic component.